ATAP News, July 2021

People think of a laser as being so precise that it passes into the language as metaphor, but users with demanding applications know that laser beams move around at a tiny scale in response to the vibrations and variability of even the most controlled lab environment.

“Missing the target by as little as a few microns can make the difference between amazing science and an unwanted addition to background noise,” said Isono.

Pointing angle offsets of less than a thousandth of a degree can result in unwanted complexities as well. That’s where diagnostic sensors and feedback systems come into play.

“A measurement that won’t interfere with the main laser beam, yet very accurately tells us about it.”
— Fumika Isono

Measuring these parameters both accurately and without intercepting the beam is the trick. Traditional methods either greatly sap the power of the beam by intercepting its pulses (which at any rate is difficult for intense, high-powered beams) or suffer inaccuracies because they are not measuring the beam exactly as delivered. The BELLA Center’s innovative approach involves splitting off and monitoring a low-powered exact copy of the main beam, reflected from the rear surface of a specially designed final optic in the beam line.

The heart of this new approach is a laser architecture with three key attributes. First, it simultaneously provides five high-power pulses and a thousand low-power pulses per second, all following the same path. Second, the beamline design is optimized to keep the high-power and low-power pulses matched in size and divergence. Finally, it replaces one of the reflective beam line mirrors with an innovative wedge-shaped reflector that has specialty coatings on both the front and the rear surfaces.

Almost all of the main beam is reflected off the front surface of the optic without otherwise being noticeably affected. A tiny bit of the beam, representing perhaps 1% of the input power, propagates through the front surface and is reflected off the rear surface. This “witness beam” goes through any subsequent optics almost in parallel to the main beam, with just enough diversion for easy placement of measurement instruments. The end result is a witness beam with pointing angle and transverse position highly correlated to those of the main beam.

The result, said Isono, is “a measurement that won’t interfere with the main laser beam, yet very accurately tells us about it.”

At the heart of the Berkeley Lab innovation is a wedge-shaped optic with a 99% reflective front surface for the main beam, and a wedged rear surface to reflect a low-powered witness beam. Both reflected beams are brought to a focus at nearly the same distance along near-identical paths, so the witness beam undergoes the same motions as the main beam.

Benefits for the BELLA Center and beyond

A near-future goal is using this diagnostic as part of a feedback system for active stabilization of the laser’s transverse position and pointing angle. Preliminary studies with the 100-terawatt laser at BELLA Center have been promising. The manuscript lays out the prospect of removing the jitters on the high-power 5 Hz laser by actively stabilizing the low-power 1 kHz laser pulse train. Laser beam vibration and motion was observed to occur on a scale of a few tens of hertz, which is well within the range of a practical feedback system. A fivefold improvement in position and angle of high-power laser pulse delivery is expected.

The development of laser-plasma particle accelerators (LPAs), which is the primary mission of the BELLA Center, exemplifies the potential benefit of this innovation. LPAs produce ultrahigh electric fields that accelerate charged particles very rapidly, thereby offering the promise of a next generation of more compact, more affordable accelerators for a wide variety of applications. Since LPAs perform their acceleration within a thin hollow structure that guides the laser, they would benefit greatly from improved control of the drive laser beam position and pointing angle.

One immediate application at the BELLA Center is the use of a laser-driven plasma accelerator (LPA) to provide electron beams for a free-electron laser (FEL) – a device that produces bright photon pulses at a far higher energy and shorter wavelength than visible light.

“The undulator, the magnetic array at the heart of the FEL, has very strict requirements on electron beam acceptance, which directly relates to the LPA drive laser pointing angle and transverse fluctuations,” said Isono.

The proposed kBELLA, a next-generation laser system that will combine high power with a kilohertz repetition rate, will be another likely application.

Interest from laser labs worldwide is anticipated. “This work is not limited to laser-plasma acceleration,” said BELLA Center Director Eric Esarey. “It addresses a specific need throughout the high-power laser community, namely, proving a correlated low-power copy of the high-power pulse without significant interference. Anywhere a high-power laser beam needs to be delivered with some precision to any application, this diagnostic is going to make a big difference. Think of laser-particle collision experiments, or laser interactions with micron-precision targets such as LPA accelerating structures or droplets.”

The work was supported by the DOE Office of Science, Office of Basic Energy Sciences, through an Early Career Research Program grant to Jeroen van Tilborg, in addition to the Office of High Energy Physics and the Gordon and Betty Moore Foundation.

To learn more…

Fumika Isono, Jeroen van Tilborg, Samuel K. Barber, Joseph Natal, Curtis Berger, Hai-En Tsai, Tobias Ostermayr, Anthony Gonsalves, Cameron Geddes, and Eric Esarey, “High-power non-perturbative laser delivery diagnostics at the final focus of 100-TW-class laser pulses,” High Power Laser Science and Engineering Volume 9, e25 (May 26, 2021), https://dx.doi:10.1017/hpl.2021.12

From ATAP’s roots comes a down-to-earth application

Team science: The paper was the cover story and Editor’s Choice of an issue of Review of Scientific Instruments, as well as the subject of an American Institute of Physics Scilight article by Yuen Yiu.
Corresponding author Mauricio Ayllon Unzueta worked with the group as part of his PhD studies in nuclear engineering at UC-Berkeley and is now a postdoctoral scholar with NASA. Other co-authors were Arun Persaud; Tanay Tak, a Summer Undergraduate Lab Internship participant who is now a graduate student at UC-Santa Barbara; research assistant Brian Mak; and Bernhard Ludewigt, an ATAP physicist who remains active in retirement.

Even for those who know about the many practical spinoff benefits of particle accelerators, the “rhizosphere” — the hidden world of plant roots and the soil — is probably not the first thing that comes to mind. It is however a tremendously important field. Most of what we eat comes directly or indirectly from plants. As the biggest single carbon reservoir on land, soil also plays a key role in keeping carbon out of the atmosphere, where it would contribute to climate change.

Their work began as one of a pair of projects awarded to Berkeley Lab in 2017 by the U.S. Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E). These innovative projects give nondestructive ways to “see” into the soil. The goal: giving farmers important information with which they can increase crop yields while also promoting carbon storage. Berkeley Lab received these competitive awards from ARPA-E’s Rhizosphere Observations Optimizing Terrestrial Sequestration (ROOTS) program.

The technique that the team adapted to this task is called associated particle imaging (API), an imaging technique based on neutron scattering. “The generator sends neutrons into the soil,” Persaud said. “Each neutron can react with atoms in the soil and generate a gamma ray, which we can detect aboveground with a gamma detector. Then we measure the energy of the gamma, and from that you can tell what kind of atom it is; carbon, iron or aluminum, for example.”

The API technique was developed decades ago and has been used for detecting explosives and special nuclear materials, as well as prospecting for diamonds and analyzing the surface materials of other planets. Key innovations for this project are the use of a fast-responding inorganic scintillator material called cerium-doped yttrium aluminum perovskite (YAP: Ce), and of a sapphire vacuum window, for a more efficient alpha detector, as well as using an all-digital readout system.

Spying on the underground: A commercial neutron tube (center of picture, under the orange panel) provides neutrons through deuterium-tritium fusion. Emitted back to back with each neutron, or “associated” with it, is an alpha particle (helium nucleus) that is picked up by a position-sensitive alpha detector. In the soil sample (shown in the bin at the bottom of the photo), the neutrons excite elements such as carbon. When this excited state relaxes, a gamma ray with energy characteristic of that element is given off. Lanthanum-bromide (LaBr) detectors, seen on the lower shelf in the photo, pick up the gamma ray. Knowing the timing of these events, and the direction of the alpha particle (and therefore the neutron), researchers can quickly piece together a 3-D picture of the composition of the soil on a centimeter scale. (Credit: Arun Persaud/Berkeley Lab)

“Measuring carbon in soil with spatial resolution, non-destructively, and in a short time has always been challenging for scientists and agriculturists alike,” said Unzueta, quoted in an American Institute of Physics science highlight article by Yuen Yiu. “The system we developed is a step forward in solving this problem with a technology that has the potential to expand to other applications such as surface composition measurements for space exploration, given that we can measure plenty of other elements as well as carbon.”

This technology will be able to not only measure how much carbon is in the soil, but also do so with spatial resolution of a few centimeters and with the potential to rapidly analyze large areas, important for potential applications to carbon management. It can be employed in the field, can measure changes over space and time without disturbing the soil, and gives real-time results. Today’s standard methods involve drilling soil cores and taking them to the lab for chemical analysis. This can take days to weeks before results are in, does not allow for repeat measurements of the same soil, and is not practical for a fine sampling grid over large areas.

Reaping benefits in other fields

The next steps in the development of this sensing technology, funded by the Laboratory-Directed R&D program, will include adapting its physical configuration to the field rather than the lab bench, as well as trying it on well characterized soil samples under the controlled conditions available with Berkeley Lab’s SMART Soils Testbed. After that, the developers hope, will come the great variety of soils in agricultural settings and ultimately evaluation of actual farm fields.

The system could greatly improve the study of carbon sequestration in soil and hence enable carbon management crucial to meeting global climate goals. Applications that circle back to the original uses of API, such as detecting explosives, drugs, and special nuclear materials, could also benefit from the development of a relatively small, lightweight, low-power-consumption device.

The work was supported by the DOE Office of Science through the ARPA-E ROOTS program.

To learn more…

Mauricio Ayllon Unzueta, Bernhard Ludewigt, Brian Mak, Tanay Tak, and Arun Persaud, “An all-digital associated particle imaging system for the 3D determination of isotopic distributions,” Review of Scientific Instruments 92 (18 June 2021), 063305, https://doi.org/10.1063/5.0030499 (final corrected version; paywalled) or https://arxiv.org/abs/2009.06768 (open access preprint on arXiv.org).

Julie Chao, “Getting to Net Zero — And Even Net Negative — is Surprisingly Feasible, and Affordable,” Berkeley Lab news release, January 27, 2021.

Click for larger version
The BELLA Petawatt beam is split into two along the beamline highlighted in green near top right. Then the portion in the Second Beamline enters a “telescope” that increases the beam size (blue). Yellow highlighting indicates the recently installed pulse compressor, whose function may be thought of as focusing in the time domain. Magenta highlighting indicates the systems shown in the photo, which perform focusing in space. The target chamber is highlighted in light red at lower left of the diagram.

The second beamline is being constructed as a DOE Accelerator Improvement Project via the Office of High Energy Physics. It will enable experiments combining two laser driven plasma accelerator stages at multi-GeV scale, as well as experiments on high brightness beam injection and controllable structures for precision beams. The R&D that it supports will advance critical aspects of plasma-based accelerators for future particle colliders and related applications.

Enabling the next steps on the road to a collider

Plasma based accelerators achieve accelerating gradients (the amount of energy added to the beam per unit of distance) thousands of times higher than conventional accelerators. The BELLA Center set a still-standing record of 8 GeV energy gain in just 20 centimeters, an energy that would have required hundreds of meters in a conventional accelerator. GeV energies enable a range of photon source applications, including mono-energetic photon sources for security and medicine, as well as compact free-electron lasers.

Realizing the potential of plasma accelerators to extend the energy frontier of high energy physics, enabling future discoveries in fundamental physics, will require collision of beams at energies of the TeV scale, a hundred times current records. Achieving these energies with efficiency, and with the beam charge that is suitable for a collider, will require combining many stages in sequence, each adding a few to 10 GeV of energy to the beam. Previous experiments showed that this is possible at lower energies.

The new second beamline will allow combination of stages at multi-GeV energies, a key step in the roadmap for plasma accelerator based future colliders. The project will split the output of the BELLA Petawatt laser, allowing the driving of two stages. Each stage will be driven by an independent laser pulse to allow control and to prototype the structure of a future collider which would use one laser per stage to distribute power requirements. Each arm has21 a separate pulse compressor, the optical system that creates the short duration pulse required to drive the plasma accelerator from the longer pulse that is amplified in the laser.

Besides staging, providing two independent laser pulses additionally enables other critical experiments that will advance the development of plasma accelerators. A second laser pulse can be used to inject a high quality particle bunch into the accelerator, or to form specially tailored plasmas that could improve the acceleration process for electrons. It could also be used to create and accelerate positrons. Each of these is required for eventual colliders and other applications.

“What I am looking forward to the most,” said Turner, “are the discussions on what enabled successful scientists to make groundbreaking discoveries or technological advances. What do they believe was the most crucial skill they acquired and what enabled them to think creatively and break the knowledge frontier?”

With interests rooted in both high-energy physics and accelerator science and technology, Turner works with the BELLA Petawatt laser and is involved in experiments with “staging”—using the output of one laser plasma accelerator as the input to another, thus achieving higher energies than a single stage could produce. This is a key step on the road to the ultimate goal of an LPA-based collider for high-energy physics. Turner is presently working with BELLA Center colleagues to set up a second beamline to facilitate these and other experiments.

Turner is one of three Berkeley Lab participants in this year’s Lindau meeting; the others are postdoctoral scholar Lindsay Bassman (Computing Sciences Area) and Michael Whittaker from the Earth and Environmental Sciences Area. All three were chosen by the University of California President’s Lindau Nobel Laureate Meeting Fellowship program, now in its second year, which includes Berkeley Lab in its selection process.

To learn more…

•  Turner’s personal and technical journey—from a childhood of car projects and robot battles to her present work with laser plasma accelerators—was the subject of a Three Questions For… feature in the February 2021 issue of ATAP News.

•  One of Turner’s fellow BELLA Center postdoctoral scholars, Lotti Obst-Huebl, gave a Lindau alumni presentation last year.

•  Learn more about Turner and the Lab’s other Lindau Nobel Laureate Meeting participants at research.lbl.gov.

Since January 2019, while studying at UC-Berkeley, Lee has interned as a student research assistant in ATAP’s Berkeley Center for Magnet Technology and Superconducting Magnet Program. Working primarily on the High Luminosity Large Hadron Collider Accelerator Upgrade Project (HL-LHC AUP) under the mentorship of ATAP staff scientist Ian Pong, he performed sample extractions and measurements of residual resistivity ratio for the niobium-tin superconducting cables; put together cable quality-control reports for committee evaluation; and developed process optimizations (such as automated spreadsheets and cost-effective sample sorters.

“I thought that my time at LBNL was supposed to be a simple data collection internship,” says Lee. “I hoped to hone my technical skills and gain some engineering experience while I decided what direction to take my career after college. Now, two and a half years later, I can say that LBNL and ATAP did all that — but to an extraordinary degree. Not only did I hone my technical skills, I acquired a host of new ones, ranging from sample prep and soldering to ADC programming and metallographic imaging. The engineering experience was not just data collection, but encompassed the creative troubleshooting of one-of-a-kind diagnostic systems, the careful handling of large databases, and all the nuances of fitting into an enormous international project.”

He found the career direction that he sought as well. At FSU, Lee will be doing his research at the Applied Superconductivity Center (ASC) and the National High Magnetic Field Laboratory (NHMFL), closely associated with the college. He will be working under the supervision of NHMFL Chief Scientist and Mechanical Engineering Professor David Larbalestier.

“I’ll always be grateful to LBNL, ATAP, and in particular Dr. Ian Pong — perhaps the best mentor I could have ever hoped to have,” says Lee.

Pong returns the compliment. “Jonathan has an insatiable appetite for knowledge and an unusual ability to grasp the key concepts,” he says, adding that he is “a fantastic team member and has shown qualities as an excellent future team leader.”

The fellowship will provide three years of funding to support Lee’s research on quality-assurance processes for high-temperature superconductors. The study may improve the performance of the material that powers fusion applications.

“For the past half-century, no one has been able to build a fusion power plant that actually produces more energy than it takes in,” Lee said. “This is changing with the industrialization of high-temperature superconductors. In order to make a difference for the world’s energy needs, tens of thousands of fusion plants will need to be built. They will need lots of magnets, and those magnets will require superconducting material that will need to be quality-assured.”

The research efforts at the NHMFL, universities, fusion startups and manufacturers are producing fusion-scale superconducting magnets that put out magnetic fields exceeding 20 Tesla. Innovations in magnet technology may make fusion an energy alternative in the future.

“The NDSEG Award will help me focus on my research so I can concentrate on being a better scientist,” Lee says. “The fellowship is important in providing mentoring opportunities and connections with fellow researchers. You never know when such connections could open a door or provide a new perspective or lead to a novel idea.”

The three-year NDSEG Fellowship is one of the most comprehensive available, covering tuition, fees, travel and more for the scholar.

The National Defense Science and Engineering Graduate (NDSEG) Fellowship is funded by the Air Force Office of Scientific Research, the Army Research Office, and the Office of Naval Research.

Kei’s key takeaways

Maximizing Flexible Work Schedules for Productivity and Safety
Kei is proud to work with so many dedicated and talented colleagues: support staff, operational coordinators, technicians, and scientists. Safety is already a high priority for all teams, as the entire BELLA Center organization meets daily to discuss work priorities, rotations, and any safety concerns from staff. Gauging individual risk tolerances and work responsibilities, Kei has maximized telework for his teams as much as possible, even going as far as tailoring a compressed work schedule for a technician who lives outside the Bay Area so that exposure during travel and while on-site can be minimized.

After the initial shelter-in-place order and before the Lab established formal occupancy protocols, he noticed personnel in one cubicle had to wear masks during Zoom meetings because they worked in the same open area. Kei took proactive action out of empathy for his team by reaching out to leaders of another group whose offices are adjacent to see if they would be open to allowing his teammates to work in their spaces with the door closed without a mask. This assertiveness has helped his team work safely and productively throughout the past year.

Simplifying Tasks and Keeping a Virtual Open-Door Policy
For the past year, Kei has been dedicated to simplifying tasks and encouraging open, responsive communications so that his team can work as efficiently as possible under the new operating limitations. One of his tactics is scheduling meetings on Mondays and Fridays to keep the days in between as open as possible for work to be done.

In lieu of scheduling even more Zoom meetings for his teams and direct reports, he maintains a virtual open-door policy where he is open and responsive to chat messages, texts, and emails from his team. To avoid email oversaturation, he defers to using whichever communication channels his direct reports are most comfortable with as he prioritizes making work as seamless and communications as open as possible. He also continuously encourages his team to take vacation days to “recharge,” and discourages weekend work and emails.

As a result of his leadership and upper management support, his team is on track to deliver on a major milestone this fiscal year as part of the BELLA iP2 project: to construct a new beamline that can provide an ultra-high intensity laser pulse to unlock new capabilities and experiments in frontier-research laser systems.

A colleague shares:
“Kei has done an excellent job keeping the work at the BELLA Center going during the pandemic. He has coordinated laser engineering work for the BELLA laser upgrades in coordination with two major projects while successfully adapting to evolving COVID work scheduling, which is no small task.”

The Council was founded on November 26, 1974 and chartered on July 18, 1975, with delegates from six campuses. The current name, “Council of University of California Staff Assemblies” (CUCSA), was adopted in 1981. Over the years, the Council has grown and now has two delegates from each location. CUCSA has conducted several projects and reported outcomes and recommendations to the President of University of California and UC administrators. Examples of recent projects include career development/succession planning, flexible work schedules, and basic staff needs.

It is an assembly of delegates dedicated to improving communications between University of California (UC) administrators and staff, and between staff at all thirteen UC locations.

One of the main goals of CUCSA is to raise issues to UC management about issues that affect policy covered UC Staff. Over the past year, we had workgroups dedicated to working in flexible work schedules, addressing basic needs of staff related to housing and food, and finding better ways to advocate for staff.

Why is it important for the Lab to have CUCSA delegates and what does being one entail?
It is important to know we are part of the UC system and have a seat at the table when important decisions are made such as paid family leave, health care, and pensions. CUCSA is a great way to network with the other campuses to discuss the issues we all face in our day-to-day jobs. Many times, something that we are working on now has been addressed by another campus which helps us not reinvent the wheel.

Being a delegate does have its requirements. First, your line manager will need to approve you becoming a delegate as there is a considerable time commitment away from your day-to-day job. CUCSA delegates meet four times a year, and each meeting is three days long. The meetings are held at one of the campuses in the UC network. Like most of us, the pandemic has made these into online Zoom sessions over three days. We hope to restart in person meetings by the end of the year.

As a delegate, you are assigned to a workgroup to focus on specific issues raised by the delegation. These workgroups meet during our quarterly meetings, and also weekly throughout the entire year, to define scope, deliverables and complete the project. At the end of the delegation year in June, each workgroup will present a presentation on their specific topic. This is our opportunity to communicate with UC management on the issues that face policy-covered staff.

At Berkeley Lab, Michelle Lee is the CUCSA sponsor and has been extremely supportive of the CUCSA delegates and our roles in the context of the systemwide efforts and LBNL. If you’re interested in becoming a CUCSA delegate, learn more on the CUCSA website.

What are you most proud of accomplishing and looking most forward to in your role as CUCSA delegates?
Our biggest accomplishment was being asked to participate in the Staff Advisory Committee to the Special Committee to Consider the Selection of the President. We worked on getting a seat on the table to be part of this committee as there were only 12 locations allowed and current CUCSA delegates are from 10 UC campuses, plus UCOP, LBNL and UCANR. That meant one of the locations would not have a seat on the committee. The call regarding this decision came to us while we were in the midst of PSPS in October 2019. We ensured that the Lab with revenue over $1 billion, collaborations with UC campuses, including joint faculty and several students should rightfully have a seat. We succeeded. Through this process, we felt that the concerns we raised to the selection committee were taken to heart. We couldn’t have a better UC President in Dr. Drake.

The other accomplishment we would like to highlight is the UC Engagement survey. Being part of this survey from start to finish and ensuring that the recommendations were brought to Lab leadership for actionable results was gratifying. The survey is conducted biannually and is an important part of ensuring staff voices are heard. The results of the survey are reviewed by the UC President. The recent CUCSA 2021 survey had a 53% response rate, an increase of 15% over the 2019 CUCSA survey. We look forward to working with Michelle Lee, CUCSA sponsor, Lady Idos, Chief Diversity Officer and Rachel Carl, Talent Manager on survey output, recommendations, and follow up action plans.

[Editor’s Note: Since the original publication of this interview, Lady Idos has been seconded to DOE’s Office of Economic Impact and Diversity to help develop their justice, equity, diversity, belonging, and inclusion strategy. Aditi Chakravarty, head of the Lab’s Learning and Organizational Development Office, will serve as Interim Chief DEI Officer to continue the progress we are making.]

Without the correct response, heat stress can progress to the more severe heat exhaustion and even heatstroke, which are life-threatening, 911-grade emergencies. Learn these warning signs and watch for them in yourself and those around you when the temperature starts climbing.

Other heat-related symptoms can include:

• Heat cramp—a muscle cramp caused by loss of body salts and fluid during sweating.
• Heat rash—a red cluster of pimples or small blisters. May appear on the neck, upper chest, in the groin, under the breasts and in elbow creases.

What To Do

If you observe the possible onset of heat exhaustion or heatstroke, you may save a life by taking action immediately:

• 911 for emergency medical assistance.
• Take steps to cool the victim (apply damp, cool towels or ice packs).
• Stay with the victim until help arrives.

To Learn More…

For further information, see EH&S Manual Chapter 40 at http://www2.lbl.gov/ehs/pub3000/CH40.html or ask your Supervisor about taking the LBNL First Aid course, EHS0116.

The July 2016 issue of the DOE’s Operating Experience Summary has detailed information on planning and conducting work in hot weather, including quantitative information about acclimatization, hydration, and the effects of clothing (more on clothing selection here).

The National Institutes of Occupational Safety and Health have useful tips on protecting against heat-related illness, including the tips in the poster shown at left.

The California Department of Industrial Relations has extensive resources on heat-related illness as well.

Julie Zhu, extension 6871 or LiZhu@lbl.gov by e-mail, is is the LBNL EH&S contact for expertise on the subject.